Holographic reflective slim virtual/augmented reality display system and method

ABSTRACT

A display method and system are disclosed for virtual/augmented reality. The method includes the steps of generating an image by a projection engine and projecting light rays defining the image onto a diffuser holographic optical element (DHOE) located between an observer and a concave mirror element, where a concave surface of the concave mirror element faces the observer. The light rays are projected onto the DHOE at a reference angle that causes the light rays to be diffused to the concave surface of the concave mirror element and the diffused light rays are reflected back to the observer such that the observer perceives a virtual image that appears to the observer at a position behind the concave mirror element and further from the observer than the concave mirror element.

CLAIM OF PRIORITY

This application claims the benefit of U.S. Provisional Application No.62/293,727 (Attorney Docket No. NVIDP1129+/16-SC-0359-US02) titled“Holographic Reflective Slim Virtual/Augmented Reality Display Systemand Method,” filed Feb. 10, 2016, the entire contents of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to display systems, and more particularlyto virtual/augmented reality display systems.

BACKGROUND

Augmented reality technology has improved, recently achieving higherresolution, increased computing power, larger eye-box size, and reducedlatency. The importance of a large eye-box is recognized to provide awide viewing window regardless of an observer's gaze position. Recently,a pinlight-based display system was developed to provide a largeeye-box, but the pinlight display system suffers from low resolution,low transparency, and image degradation due to diffraction. There is aneed for addressing these issues and/or other issues associated with theprior art.

SUMMARY

A method and system are disclosed for displaying virtual/augmentedreality content. The method includes the steps of projecting light raysonto a diffuser holographic optical element (DHOE) located between anobserver and a concave mirror element, where a concave surface of theconcave mirror element faces the observer. The light rays are projectedonto the DHOE at a reference angle that causes the light rays to bediffused to the concave surface of the concave mirror element and thediffused light rays are reflected back to the observer such that theobserver perceives a virtual image that appears to the observer at aposition behind the concave mirror element and further from the observerthan the concave mirror element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a flowchart of a method for displayingvirtual/augmented reality content, in accordance with one embodiment;

FIG. 1B illustrates a diffuser holographic optical element (DHOE), inaccordance with the prior art;

FIG. 1C illustrates a DHOE and concave mirror array, in accordance withthe prior art

FIG. 2A illustrates a diagram of a virtual/augmented reality displaysystem, in accordance with one embodiment;

FIG. 2B illustrates an annotated diagram of the virtual/augmentedreality display system shown in FIG. 2A, in accordance with oneembodiment;

FIG. 2C illustrates another diagram of a virtual/augmented realitydisplay system, in accordance with one embodiment;

FIG. 3A illustrates a diagram of a virtual/augmented reality displaysystem including a light guide, in accordance with one embodiment;

FIG. 3B illustrates a diagram of a virtual/augmented reality displaysystem including a dichroic concave mirror, in accordance with oneembodiment;

FIG. 3C illustrates a diagram of another virtual/augmented realitydisplay system including a light guide, in accordance with oneembodiment;

FIG. 4A illustrates a virtual/augmented reality head-mounted displaysystem, in accordance with one embodiment;

FIG. 4B illustrates another view of the virtual/augmented realityhead-mounted display system shown in FIG. 4A, in accordance with oneembodiment;

FIG. 4C illustrates an annotated diagram of the virtual/augmentedreality display system, in accordance with one embodiment;

FIG. 4D illustrates an annotated diagram of a conventional liquidcrystal virtual reality display system, in accordance with the priorart;

FIG. 4E illustrates a projection engine, in accordance with oneembodiment;

FIG. 5A illustrates a flowchart of another method for displayingvirtual/augmented reality content, in accordance with one embodiment;

FIG. 5B illustrates a flowchart of yet another method for displayingvirtual/augmented reality content, in accordance with one embodiment;and

FIG. 6 illustrates an exemplary system in which the various architectureand/or functionality of the various previous embodiments may beimplemented.

DETAILED DESCRIPTION

The present disclosure describes an augmented reality (AR) displaysystem with high resolution, a sufficiently large eye-box so that gazetracking is not needed, and high transparency for clear viewing ofoutside scenes and the projected image. The AR display system relies ona diffuser and a concave mirror. In one embodiment, the diffuser is adiffuser holographic optical element (DHOE). Light rays diffracted bythe diffuser are reflected by the concave mirror, and the reflectedlight is goes through the diffuser without refraction and reaches anobserver.

A DHOE, was first introduced in a frontal projection 3D display systemdescribed by Yeom et. al. in 2014 (J. Yeom, J. Jeong, C. Jang, K. Hong,S.-g. Park, and B. Lee, “Reflection-type integral imaging system using adiffuser holographic optical element,” Opt. Express 22, 29617-29626).The DHOE is a holographic optical element that functions as atransmissive diffuser only for a reference wave, and functions as atransparent medium for other light waves. By taking advantage of theangular (and spectral) selectivity characteristics of DHOEs, areflective-type AR display system can be achieved.

FIG. 1A illustrates a flowchart of a method 100 for displaying images bya virtual/augmented reality system, in accordance with one embodiment.Although method 100 is described in the context of a DHOE and a concavemirror element, the method 100 may also be performed using additionalcomponents, such as a light guide. Furthermore, persons of ordinaryskill in the art will understand that any system that performs method100 is within the scope and spirit of embodiments of the presentinvention.

At step 105, an image is generated by a projection engine. In oneembodiment, the image is elemental images including a two-dimensionalarray of images of a scene or object that are each generated from adifferent viewpoint, so that when the images are viewed in combination,a three-dimensional virtual image of the scene or object appears. Inanother embodiment, the image is a complete image (i.e., a singleimage). At step 110, light rays defining the image are projected onto adiffuser holographic optical element (DHOE) located between an observerand a concave mirror element, where a concave surface of the concavemirror element faces the observer. In one embodiment, light raysdefining an image are projected away from the observer and towards theDHOE and the concave surface of the concave mirror element. In anotherembodiment, light rays defining an image are projected towards theobserver and the DHOE and away from the concave surface of the concavemirror element.

The light rays are projected onto the DHOE at a reference angle thatcauses the light rays to be diffused to the concave surface of theconcave mirror element. At step 120, the DHOE diffuses the light rays tothe concave surface of the concave mirror element. In one embodiment,the concave mirror element is a half-mirror. In one embodiment, theconcave mirror element is a full mirror. In one embodiment, the concavemirror element is a wavelength selective half or full mirror.

At step 130, the diffused light rays are reflected back to the observersuch that the observer perceives a virtual image that appears to theobserver at a position behind the concave mirror element and furtherfrom the observer than the concave mirror element. More specifically,the diffused light rays output from the DHOE are reflected by theconcave mirror element and travel back to the DHOE. However, due to theangular selectivity characteristics of the DHOE, the reflected lightrays pass through the DHOE without any optical distortion, and reach theobserver's eye. In one embodiment, the virtual image is a larger versionof the image generated by the projection engine at step 105.

In one embodiment, an additional light guide is included between theobserver and the DHOE to fold the optical path by internal reflectionand ensure sufficient projection distance with reduced viewing distanceand eye relief. Reduced eye relief is crucial to make a HMD with asmaller form factor and sufficient projection distance is needed toprovide a sufficiently large virtual image.

In one embodiment, a wavelength-selective dichroic mirror can be used asthe concave mirror element. The wavelength-selective dichroic mirrorprovides higher efficiency, transparency, and security by keeping lightrays emitted by a projector within the virtual/augmented reality system,so that displayed information cannot be viewed from outside thevirtual/augmented reality system. In one embodiment, a projector (suchas laser projector) configured to generate the wavelength(s) selectivelyreflected by the wavelength-selective dichroic mirror is used togenerate the light rays. The dichroic mirror selectively reflects onlythe specific wavelengths of light rays generated by the wavelengthselective projector and does not reflect other wavelengths. Such awavelength selective embodiment can shield wavelengths used by theprojector from the virtual/augmented reality system while protecting theprivacy of the observer's displayed information.

More illustrative information will now be set forth regarding variousoptional architectures and features with which the foregoing frameworkmay or may not be implemented, per the desires of the user. It should bestrongly noted that the following information is set forth forillustrative purposes and should not be construed as limiting in anymanner. Any of the following features may be optionally incorporatedwith or without the exclusion of other features described.

FIG. 1B illustrates a DHOE 140, in accordance with the prior art. TheDHOE 140 is a one-directional angular wavelength selective diffuser. TheDHOE 140 is configured by recording a one-directional diffuser to a HOEusing a reference wave 145 from a particular point or particular angle.The HOE then functions as a diffuser for light rays received from theparticular point or particular angle. Therefore, when a projector islocated at the exact point or a point near where the reference waveoriginated, then the light rays from the projector are diffused by theDHOE 140, and an observer at the opposing side of the DHOE 140 (on theright side facing the DHOE 140 in FIG. 1B) can see a clear imageproduced by the diffused light rays.

However, for light rays intersecting the DHOE 140 from other directions,such as light rays 115 and 125, the DHOE 140 functions as a transparentmedium. The DHOE 140 does not affect light rays projected onto opposingside of the DHOE 140 or light rays intersecting the DHOE 140 from anangle that does not equal or is not close to the angle of the referencewave 145. The DHOE 140 is a special type of diffuser that utilizesangular selectivity and transparency characteristics. Thecharacteristics originate from the holographic nature of the DHOE 140and cannot be achieved with conventional optical elements such aslenses, mirrors, diffusers, or a combination of conventional opticalelements. The light rays that diffract from the DHOE 140 satisfy theBragg matching condition or are a close approximation to satisfying theBragg condition. Operation of the DHOE 140 is based on a position of theprojector or angle of the input light rays depends on the thickness ofthe holographic film used to create the DHOE. A thinner holographic film(such as 20 microns) will accept a larger range of input angles than athicker holographic film (such as 100 microns). Similarly, operation ofthe DHOE 140 changes based on a depth of the index of refractionmodulation of the holographic film.

FIG. 1C illustrates a three-dimensional (3D) display system 150including the DHOE 140 and a concave mirror array 155, in accordancewith the prior art. Light rays define elemental images to produce a 3Dpixel 165 and additional 3D pixels of a 3D image (not shown). The DHOE140 diffuses the light rays intersecting the DHOE 140 from the angle ofthe reference wave 145 and the concave mirror array 155 reflects thediffused light rays to produce the 3D pixel 165 and the additional 3Dpixels of the 3D image. Light rays reflected from two or more of theconcave mirrors in the concave mirror array 155 are integrated to formeach 3D pixel. Note that the 3D image, including the 3D pixel 165appears to an observer 160 at a position in front of the DHOE 140 and infront of the concave mirror array 155. Importantly, the 3D displaysystem 150 is configured for a desktop viewing regime and is notsuitable for a head-mounted or near to eye display regime.

FIG. 2A illustrates a diagram of a virtual/augmented reality displaysystem 200, in accordance with one embodiment. In contrast with the 3Ddisplay system 150, a virtual image 215 appears to an observer 230behind a DHOE 220 and behind a concave mirror element 210. The DHOE 220,was recorded with a diverging reference wave, and is located in front ofthe observer 230 and between the observer 230 and the concave mirrorelement 210. A projector 225 is located at the position where thereference wave light source was located (i.e., where the reference waveoriginated). The projector 225 generates divergent light rays definingan image and the image is diffused in the forward direction at the DHOE220. In one embodiment, the projector 225 comprises multiple projectiondevices, where each projection device generates a portion of the image.In one embodiment, the divergent light rays generated by the projector225 are redirected using one or more mirrors or other optical device(s)to reach the DHOE 220. The light is diffused through the DHOE 220 suchthat the DHOE 220 is illuminated with the image projected by theprojector 225. The image is then reflected off the concave mirrorelement 210 and reflected back through the DHOE 220 to be directed atthe observer 230.

The DHOE 220 is recorded with the reference wave light source divergingfrom a position of the projector 225 and the signal wave originatingfrom a diffuser. Therefore, the DHOE 220 diffuses only the light raysoriginating from the projector 225. Light rays 205 propagating towardsthe DHOE 220 from behind or from directions that do not originate at theprojector 225 pass through the DHOE 220 without being diffused (andwithout any optical distortion). The diffused light output by the DHOE220 is reflected at the concave mirror element 210. In one embodiment,both sides of the concave mirror element 210 have the same radius ofcurvature and a surface of the concave mirror element 210 facing theDHOE 220 is coated so that the concave mirror element 210 is a concavehalf mirror.

The concave mirror element 210 forms a virtual image 210 at infinitywhen a distance a, between the concave mirror element 210 and the DHOE220 is equal to a focal length f, of the concave mirror element 210.When the focal length f is longer than the distance a, thevirtual/augmented reality display system 200 forms the virtual image 215at a large virtual plane behind the concave mirror element 210 that iscloser than infinity. In one embodiment, f is set to be slightly largerthan a, so the image diffused from DHOE surface forms an enlargedvirtual image 215 at a distance b beyond the concave mirror element 210.The distance b is decided by a simple lens equation:

1/f=1/a−1/b.

The virtual/augmented reality display system 200 produces a sufficientlylarge eye-box without gaze tracking, thereby providing a clear imageregardless of the observer's 230 gaze direction. Even with pupilmovement, the observer 230 can see the virtual image 215 because thelight rays are scattered from DHOE 220.

FIG. 2B illustrates an annotated diagram of the virtual/augmentedreality display system 200, in accordance with one embodiment. Theviewing characteristics of the virtual/augmented reality display system200 may be analyzed with geometral optics for a viewing angle θ_(v) andeye-box size e. In other embodiments, the viewing characteristics maydiffer due to varying geometry and/or configurations of the components(e.g., concave mirror element 210, projector 225, and DHOE 220) as wellas the inclusion of one or more additional components. As shown in FIG.2B, v is the viewing distance or eye relief and R is the reflectance ofthe concave mirror element 210.

The width of the projected image on the DHOE 220, w can be derived fromthe projector 225 position and projection direction as follows:

$\begin{matrix}{w = {d\left\lbrack {{\tan\left( {\theta_{r} + \frac{\theta_{p}}{2}} \right)} - {\tan\left( {\theta_{r} - \frac{\theta_{p}}{2}} \right)}} \right\rbrack}} & (1)\end{matrix}$

where d is a projection distance, θ_(r) is a reference wave angle, andθ_(p) is an output angle of the projector 225. The magnification m ofthe virtual image 215 that is enlarged by the concave mirror element 210can be derived from Gauss's law as m=|b/a|=f/(f−a), and a size I, of thevirtual image 215 is derived as I=mw=fw/(f−a). The viewing angle θ_(v)is determined from the virtual image size I and the distance between theimage and the eye as follows:

$\begin{matrix}{{\tan\left( \frac{\theta_{v}}{2} \right)} = {\frac{I/2}{v + a + b} = {\frac{{fd}/2}{\left( {f - a} \right)\left( {v + a + b} \right)}\left\lbrack {{\tan\left( {\theta_{r} + \frac{\theta_{p}}{2}} \right)} - {\tan\left( {\theta_{r} - \frac{\theta_{p}}{2}} \right)}} \right\rbrack}}} & (2)\end{matrix}$

The eye-box size e can be determined by the critical rays of diffractedlight: the innermost ray from outermost image pixel on the DHOE 220. Byassuming that the last pixel at the bottom border on the DHOE 220 planeis located on a first point (0, −w/2), the innermost ray from the firstpoint travels to the surface of the concave mirror element 210 and isreflected at a second point (a, −w/2+a*tan(θ_(d)/2)), where θ_(d) is theangle through which rays are diffracted by the DHOE 220. The reflectedcritical ray travels back to the observer 230 and reaches to the borderof the eye-box. The eye-box size e can be derived as follows:

$\begin{matrix}{\frac{e}{2} = {{\left( {a + v} \right){\tan\left( {\frac{{{a{\; \;}{\tan \left( \frac{\theta_{d}}{2} \right)}} - \frac{w}{2}}}{f} + \frac{\theta_{d}}{2}} \right)}} - {{{a\mspace{14mu} {\tan\left( \frac{\theta_{d}}{2} \right)}} - \frac{w}{2}}}}} & (3)\end{matrix}$

Note that the eye pupil size and the gaze direction are not consideredbecause the virtual/augmented reality display system 200 can provide thesame quality image across any gaze angle within the eye-box e.

FIG. 2C illustrates another diagram of a virtual/augmented realitydisplay system 250, in accordance with one embodiment. Compared with thevirtual/augmented reality display system 200, a projector 275 is locatedat a second position that is further from the observer 230 compared witha DHOE 270. In one embodiment, the projector 275 is located between theDHOE 270 and the concave mirror element 210. In contrast with thetransmissive diffuser DHOE 220, the DHOE 270 is a reflective diffuser sothat light rays are reflected and diffused at the surface of the DHOE270. A virtual image appears to the observer 230 behind the DHOE 270 andbehind the concave mirror element 210.

The DHOE 270, was recorded with a diverging reference wave and theprojector 275 is located at the second position where the reference wavelight source was located to record the DHOE 270 (i.e., where thereference wave originated). The projector 275 generates divergent lightrays defining an image and the image is diffused in the reversedirection at the DHOE 270. The light is diffused at the DHOE 270 suchthat the back side (i.e., the side facing the concave mirror element210) of the DHOE 270 is illuminated with the image projected by theprojector 275. The image is then reflected off the concave mirrorelement 210 and reflected back through the DHOE 270 to be directed atthe observer 230.

FIG. 3A illustrates a diagram of a virtual/augmented reality displaysystem 300 including a light guide 320, in accordance with oneembodiment. In one embodiment, the light guide 320 is a wave guide. Thevirtual/augmented reality display system 300 also includes the projector225, the DHOE 220, and the concave mirror element 210 used in thevirtual/augmented reality display system 200. In one embodiment, anindex matched concave mirror replaces the concave mirror element 210 sothat the concave mirror element 210 is at least partially transparent.In one embodiment, the overall transparency of the index matched concavemirror is greater than 90%.

As shown in FIG. 3A, the light guide 320 is a wedge shaped wave guide ora wedge prism. Alternatively, in one embodiment, the light guide 320 isbased on free-form optics, such as a prism having one or more free-formsurfaces. The virtual/augmented reality display system 300 requiressufficient projection distance to provide a large enough image to theDHOE 220. The light guide 320 is positioned between the observer 230 andthe DHOE 220 and configured increase the projection distance by foldingthe optical path using internal reflection within the light guide 320.The folded light rays are diffused by the DHOE 220 and then reflected bythe concave mirror element 210. The reflected light rays then passthrough the DHOE 220 without being diffused and the light rays passthrough the light guide 320 to reach the observer 230 without beingreflected within the light guide 320.

Folding the optical path reduces eye relief, reduces a viewing distancev′ and increases a viewing angle θ_(d)′. In the context of the followingdescription, eye relief is the distance between the eye and the firstoptical component in front of the eye. Reduced eye relief may be crucialto implement the virtual/augmented reality display system 300 in ahead-mounted or wearable form factor. Furthermore, as shown in Equation(2), the viewing angle is closely related to the viewing distance v, anda larger viewing angle can be achieved with the wedge-shaped wave guide.

FIG. 3B illustrates a diagram of a virtual/augmented reality displaysystem 350 including a dichroic concave mirror 310, in accordance withone embodiment. In one embodiment, the dichroic concave mirror 310 is awavelength-selective dichroic concave mirror. As shown in FIG. 3B, thewavelengths may correspond to an RGB spectrum. The virtual/augmentedreality display system 350 also includes the DHOE 220 and the lightguide 320 used in the virtual/augmented reality display system 300. Theprojector 225 is replaced with a projector 325, such as a laserprojector, that is configured to generate light rays having wavelengthsthat are reflected by the dichroic concave mirror 310.

In one embodiment, the projector 325 may include a white light sourcepositioned behind one or more lenses, light modulating elements (e.g.,liquid crystal panels), and color filter arrays. The projector 325 isconfigured to modulate a wavelength of light projected onto a surface ofthe light guide 320 by controlling the various elements enumeratedabove.

The dichroic concave mirror 310 is a wavelength-selective concave mirrorthat is coated on the concave surface, where the reflection wavelengthsare matched with the wavelengths of the light rays generated by theprojector 325. In other words, the wavelength-selective dichroic concavemirror 310 is paired with the projector 325. For example, thewavelength-selective dichroic concave mirror 310 may reflect light ofwavelengths corresponding to a first color band, a second color band,and a third color band. The wavelength-selective dichroic concave mirror310 may not reflect light of wavelengths that do not correspond to thefirst color band, the second color band, or the third color band. Theprojector 325 may then project light rays to form an image with light ineach of the three color bands. In one embodiment, the three color bandsare associated with red, green, and blue colors.

Relative to an embodiment that combines the concave mirror element 210with a broadband beamsplitter coating, using the projector 325 and thewavelength-selective dichroic concave mirror 310 increases thereflectance R of the dichroic concave mirror 310, for those wavelengthsreflected by the dichroic concave mirror 310, so that more lightgenerated by the projector 325 is reflected from the DHOE 220 and thelight generated by the projector 325 is prevented from exiting thevirtual/augmented reality display system 350, hiding the displayedcontent from outside observers. A high transparency T of most of thetransmitted wavelengths of light is maintained.

FIG. 3C illustrates a diagram of another virtual/augmented realitydisplay system 360 including a light guide 380, in accordance with oneembodiment. Compared with the virtual/augmented reality display system300, a projector 375 is located at a second position that is furtherfrom the observer 230 compared with a DHOE 370. In one embodiment, theprojector 375 is located between the DHOE 370 and the concave mirrorelement 210. The DHOE 370 is a reflective diffuser so that light raysare reflected and diffused at the surface of the DHOE 370. A virtualimage appears to the observer 230 behind the DHOE 370 and behind theconcave mirror element 210. As shown in FIG. 3C, the light guide 380 isa wedge shaped wave guide or a wedge prism. The virtual/augmentedreality display system 360 requires sufficient projection distance toprovide a large enough image to the DHOE 370. The light guide 380 ispositioned between the projector 375 and the DHOE 220 and configuredincrease the projection distance by folding the optical path usinginternal reflection.

The DHOE 370 was recorded with a diverging reference wave and theprojector 375 is located at the second position where the reference wavelight source was located to record the DHOE 370 (i.e., where thereference wave originated). The projector 375 generates divergent lightrays defining an image and the light rays are folded by the light guide380 before the image is diffused in the reverse direction at the DHOE370. The folded light rays are diffused at the DHOE 370 such that theback side (i.e., the side facing the concave mirror element 210) of theDHOE 370 is illuminated with the image projected by the projector 375.The image is then reflected off the concave mirror element 210 andreflected back through the DHOE 370 to be directed at the observer 230.In one embodiment, the projector 375 is replaced with the projector 325and the concave mirror element 210 is replaced with the dichroic concavemirror 310.

FIG. 4A illustrates a virtual/augmented reality head-mounted displaysystem 400, in accordance with one embodiment. The virtual/augmentedreality head-mounted display system 400 is implemented in a glasses-typeform factor and includes several components: two projectors 225, twolight guides 320, two DHOEs 220, and two concave mirror elements 210.The two projectors 225 may be configured to project stereo images toproduce a 3D image. An eyeglass frame apparatus supports the componentsand is configured to cover one or both eyes of the observer 230.

The light guides 320 reduce the space between the observer and the DHOEto be reduced for implementation in the glasses-type form factor. Thevirtual/augmented reality head-mounted display system 400 is astereoscopic virtual/augmented reality head-mounted display system. Inone embodiment, the projectors 225 and concave mirror elements 210 arereplaced with the projectors 325 and concave mirror elements 310,respectively. In one embodiment, the virtual/augmented realityhead-mounted display system 400 is implemented in monocle glasses-typeform and only a single projector 225, light guide 320, DHOE 220, andconcave mirror element 210 are included. In one embodiment, the DHOEs220 are replaced with the DHOE 270 or 370, the light guides 320 arereplaced with the light guides 380 and the projectors 225 are positionedbetween the light guides 380 and the concave mirror elements 210 toproject light rays toward the DHOEs 270 or 370.

FIG. 4B illustrates another view of the virtual/augmented realityhead-mounted display system 400 shown in FIG. 4A, in accordance with oneembodiment. The virtual/augmented reality head-mounted display system400 may be used as a virtual reality display when the two concave mirrorelements 210 are complete mirrors so that all light from the environment(i.e., not generated by the projectors 225) is blocked.

The virtual/augmented reality display systems 200, 300, 350 and thehead-mounted display system 400 may be compared to conventional virtualreality (VR) systems. For example, a conventional VR system typicallyincludes a liquid crystal display (LCD) or organic light emitting diode(OLED) display and a convex lens. Two important differences between thevirtual/augmented reality display systems 200, 300, 350 and thehead-mounted display system 400 and conventional VR systems are that aconcave mirror is used rather than a convex lens and the image isdisplayed using a projector and diffuser instead of an LCD or OLEDdisplay. FIG. 4C illustrates an annotated diagram of a virtual/augmentedreality display system 440, in accordance with one embodiment.

FIG. 4D illustrates an annotated diagram of a conventional LCD virtualreality display system 450, in accordance with the prior art. Theconventional virtual reality display system 450 includes an LCD 460 anda convex lens 470. In contrast, the virtual/augmented reality displaysystem 440 includes the projector 225, DHOE 220, and the concave mirrorelement 210.

As shown in FIGS. 4C and 4D, the optical elements of both theconventional LCD virtual reality display system 450 and the opticalelements of the virtual/augmented reality display systems 200, 300, 350and the head-mounted display system 400 may be configured in a similartopology. The focal length f of the concave mirror element 210 equalsthe focal length of a convex lens 470. The distance a between the DHOE220 and the concave mirror element 210 equals the distance between theconvex lens 470 and the LCD 460. As a result, an observed image 445generated by the virtual/augmented reality display system 440 is similarin size and resolution as an observed image 465 generated by theconventional LCD virtual reality display system 450. The distance bbetween the concave mirror element 210 and the observed image 445 equalsa distance between the convex lens 470 and the observed image 465.

Additional differences between the virtual/augmented reality displaysystem 440 and the conventional LCD VR system 450 are mass, center ofmass, aberration, and curvature characteristics. The LCD 460 and convexlens 470 are typically heavier than the projector 225, DHOE 220, and theconvex mirror element 210. Furthermore, the LCD 460 is the heaviestcomponent in the conventional LCD VR system 450 so that most of the massis distributed in further from the observer 430. In thevirtual/augmented reality display system 440, the mass is distributedcloser to the observer 230 so the virtual/augmented reality displaysystem 440 may be easier and more comfortable to wear (i.e., as an HMDwithout a strap around the back of the head). When the projector 225 isthe heaviest component in the virtual/augmented reality display system440, the weight is distributed closer to the observer 230, reducing thetorque so that a glasses-type form factor may be used to implement thevirtual/augmented reality display system 440.

Additionally, lenses are prone to image degradation due to chromaticaberration and distortions whereas mirrors do not cause imagedegradation due to chromatic aberration and distortions. Mirrors arealso more light efficient compared conventional lenses and/or prismsbecause refraction causes some light loss (e.g., fresnel losses), andlight loss increases with optical path length (i.e., bulk absorption).Fresnel losses, R_(f)=(n−1)²/(n+1)², where n is the ratio of two mediumswhere refraction occurs, n=n₂/n₁. R_(f) is typically 4-5% forPoly(methyl methacrylate) PMMA material and R_(f) is slightly lower forOptical Glass (e.g., BK7). Bulk absorption, T_(b)=T₀*exp(−d/λ), where λis the wavelength of the light, d is the thickness of the material, andT₀ is the optical transparency of the material at the wavelength λ. Incontrast, mirrors can be made that are 99.99999% efficient. Therefore,the concave mirror element 210 provides a superior image in terms ofquality compared with the convex lens 470. Finally, given the samecurvature, R, the focal length f, for the concave mirror element 210 isapproximately half that of the convex lens 470. Therefore, to achievesame optical power a much thicker concave lens 470 is needed, which cancause additional spherical aberration.

FIG. 4E illustrates a projection engine 410, in accordance with oneembodiment. The projection engine 410 that may be included within theprojector 225, 275, 325, or 375 or, as shown in FIG. 4E, coupled to theprojector(s) 225, 275, 325, or 375. The projection engine 410 includeselectronics for generating images and the projector 225, 275, 325, or375 modulates a light source (included in the projector) to project theimages to the DHOE 220, 270, or 370 or the light guide 320 or 380. Inone embodiment, the projector 225, 275, 325, or 375 comprises multipleprojection devices, where each projection device generates a portion ofan image. In one embodiment, the divergent light rays generated by theprojector 225, 275, 325, or 375 are redirected using one or more mirrorsor other optical device(s) to reach the 220, 270, or 370 or the lightguide 320 or 380. In one embodiment, the projection engine 410 includesa processor 415, a memory 435, an interface 455, a power managementintegrated circuit (PMIC) 425, and a battery 475. The processor 415 andmemory 435 may be implemented in a single package configuration (e.g.,package-on-package (POP)) and affixed via solder to a printed circuitboard (PCB) that includes the interface 455 and PMIC 425 affixedthereto. The battery 475 may be a lithium ion battery, which may berecharged using the PMIC 425 when the virtual/augmented realityhead-mounted display system 400 is connected to an external powersource. Alternatively, the battery 475 may be a disposable coin-typebattery that can be replaced when the battery 475 is drained of charge.

In one embodiment, the interface 455 comprises a controller thatimplements a wireless communications standard such as IEEE 802.15 (i.e.,Bluetooth) or IEEE 802.11 (i.e., Wi-Fi). The controller may include oneor more transceivers and an antenna array consisting of one or moreantennas for transmitting or receiving data via wireless channels. Thecontroller may also include an on-chip memory for storing data receivedfrom the processor 415 for transmission over the wireless channels ordata to be transmitted to the processor 415 received over the wirelesschannels. In another embodiment, the interface 455 comprises acontroller that implements a wired communications standard such as a USBinterface. The interface 455 may include a physical interface forplugging a cable into the virtual/augmented reality head-mounted displaysystem 400 as well as a controller for managing communications over thecommunications channel(s).

In one embodiment, the processor 415 receives image data to be displayedon the virtual/augmented reality head-mounted display system 400 via thechannels connected to the interface 455. The image data may be stored inthe memory 435. The processor 415 may also implement algorithms formodifying the image data in the memory 435. For example, the processor415 may warp the image data based on parameters stored in the memory 435that map the image data to an observer's retina based on characteristicsof the observer's eye. For example, the parameters may enable image datato be warped to accommodate a corrective lens prescription for anobserver so that the display can be seen without corrective lenses. Inanother embodiment, the processor 415 receives instructions and/or dataand is configured to generate image data for display. For example, theprocessor 415 may receive 3D geometric primitive data to be renderedbased on the instructions to generate the image data in the memory 435.The image data may then be transmitted to the projector 225, 275, 325,or 375, which modulates a light source to project light to the DHOE 220,270, or 370 or the light guide 320 or 380.

It will be appreciated that the projection engine 410 described andshown in FIG. 4E is only one such example of the projection engine 410.Other embodiments of the projection engine 410 are contemplated as beingwithin the scope of the present disclosure, including but not limited todifferent light modulating technology such as laser projection; anapplication specific integrated circuit (ASIC) that includes theprocessor 415, memory 435, PMIC 425, and/or interface 455 on a singledie; and a more complex system with multiple processors (e.g., CPU andGPU) as well as other components in addition to or in lieu of thecomponents shown in FIG. 4E.

FIG. 5A illustrates a flowchart of another method 500 for displayingvirtual/augmented reality content, in accordance with one embodiment.Persons of ordinary skill in the art will understand that any systemthat performs method 500 is within the scope and spirit of embodimentsof the present invention.

At step 505, light rays are projected by the projector 325 through thelight guide 320 to fold a path of the light rays using internalreflection. At step 510, the folded light rays are projected onto theDHOE 220 that is located between the observer 230 and the concave mirrorelement 210. At step 520, the DHOE 220 diffuses the light rays to theconcave surface of the concave mirror element 210. In one embodiment,the concave mirror element 210 is a half-mirror. In one embodiment, theconcave mirror element is a full mirror. In one embodiment, the concavemirror element 210 is a wavelength-selective half or full mirror, suchas the dichroic concave mirror 310 and the projector 225 is replacedwith a projector, such as projector 325.

At step 530, the diffused light rays are reflected back to the observer230 such that the observer perceives a virtual image that appears to theobserver 230 at a position behind the concave mirror element 210 andfurther from the observer than the concave mirror element 210. In oneembodiment, the DHOE 220 is replaced with the DHOE 370, the light guide320 is replaced with the light guide 380, and the projector 325 isreplaced with the projector 375.

FIG. 5B illustrates a flowchart of yet another method 540 for displayingvirtual/augmented reality content, in accordance with one embodiment.Persons of ordinary skill in the art will understand that any systemthat performs method 540 is within the scope and spirit of embodimentsof the present invention.

At step 545, light rays are generated at a first wavelength. At step550, the light rays at the first wavelength are projected by theprojector 325 through the light guide 320 to fold a path of the lightrays using internal reflection. At step 560, the DHOE 270 diffuses thelight rays at the first wavelength to the concave surface of thedichroic concave mirror 310. In one embodiment, the DHOE 270 does notdiffuse light rays that are not at the first wavelength to the concavesurface of the dichroic concave mirror 310. At step 570, the diffusedlight rays are reflected back to the observer 230 such that the observerperceives a virtual image that appears to the observer 230 at a positionbehind the dichroic concave mirror 310 and further from the observerthan the dichroic concave mirror 310. In one embodiment, the dichroicconcave mirror 310 is configured to reflect only light rays of the firstwavelength. In one embodiment, light rays at least one additionalwavelength are projected by the projector 325 through the light guide320 and the DHOE 270 diffuses the light rays at the at least oneadditional wavelength and does not diffuse light rays that are not atthe at least on additional wavelength. In one embodiment, the DHOE 270is replaced with the DHOE 370, the light guide 320 is replaced with thelight guide 380, and the projector 325 is replaced with the projector375.

The virtual/augmented reality display systems 200, 300, 350, 400, and440 each produce high resolution images and a large eye-box is providedwithout gaze or pupil tracking. Therefore, the observer 230 can view aclear two-dimensional image, even during saccade or eye judder. Usingthe concave mirror element 210 instead of a lens enables thevirtual/augmented reality display systems 200, 300, 350, 400, and 440 tobe free from chromatic aberrations and lens distortion and reducesspherical aberration. The virtual/augmented reality display systems 200,300, 350, and 440 may be implemented as a wearable device, as shown inFIGS. 4A and 4B to provide a virtual reality experience (when theconcave mirror elements 210 are full mirrors) or to provide an augmentedreality experience with high transparency (when the concave mirrorelements 210 are half mirrors or wavelength-selective mirrors).

Exemplary System

FIG. 6 illustrates an exemplary system 600 in which the variousarchitecture and/or functionality of the various previous embodimentsmay be implemented. The exemplary system 600 may be used to implement avirtual/augmented reality display system 250. As shown, a system 600 isprovided including at least one central processor 601 that is connectedto a communication bus 602. The communication bus 602 may be implementedusing any suitable protocol, such as PCI (Peripheral ComponentInterconnect), PCI-Express, AGP (Accelerated Graphics Port),HyperTransport, or any other bus or point-to-point communicationprotocol(s). The system 600 also includes a main memory 604. Controllogic (software) and data are stored in the main memory 604 which maytake the form of random access memory (RAM).

The system 600 also includes input devices 612, a graphics processor606, and a display 608, i.e. a conventional CRT (cathode ray tube), LCD(liquid crystal display), LED (light emitting diode), plasma display orthe like. In one embodiment, the display 608 is a display including atleast the DHOE 220 and the concave mirror element 210, the DHOE 220 andthe index matched concave mirror element 310, or the DHOE 220 and the3-color dichroic concave mirror element 310. In one embodiment, thedisplay 608 is implemented in a head-mounted display form factor. Userinput may be received from the input devices 612, e.g., keyboard, mouse,touchpad, microphone, and the like. In one embodiment, the graphicsprocessor 606 may include a plurality of shader modules, a rasterizationmodule, etc. Each of the foregoing modules may even be situated on asingle semiconductor platform to form a graphics processing unit (GPU).

In the present description, a single semiconductor platform may refer toa sole unitary semiconductor-based integrated circuit or chip. It shouldbe noted that the term single semiconductor platform may also refer tomulti-chip modules with increased connectivity which simulate on-chipoperation, and make substantial improvements over utilizing aconventional central processing unit (CPU) and bus implementation. Ofcourse, the various modules may also be situated separately or invarious combinations of semiconductor platforms per the desires of theuser.

The system 600 may also include a secondary storage 610. The secondarystorage 610 includes, for example, a hard disk drive and/or a removablestorage drive, representing a floppy disk drive, a magnetic tape drive,a compact disk drive, digital versatile disk (DVD) drive, recordingdevice, universal serial bus (USB) flash memory. The removable storagedrive reads from and/or writes to a removable storage unit in awell-known manner.

Computer programs, or computer control logic algorithms, may be storedin the main memory 604 and/or the secondary storage 610. Such computerprograms, when executed, enable the system 600 to perform variousfunctions. The memory 604, the storage 610, and/or any other storage arepossible examples of computer-readable media. Data streams associatedwith gestures may be stored in the main memory 604 and/or the secondarystorage 610.

In one embodiment, the architecture and/or functionality of the variousprevious figures may be implemented in the context of the centralprocessor 601, the graphics processor 606, an integrated circuit (notshown) that is capable of at least a portion of the capabilities of boththe central processor 601 and the graphics processor 606, a chipset(i.e., a group of integrated circuits designed to work and sold as aunit for performing related functions, etc.), and/or any otherintegrated circuit for that matter.

Still yet, the architecture and/or functionality of the various previousfigures may be implemented in the context of a general computer system,a circuit board system, a game console system dedicated forentertainment purposes, an application-specific system, and/or any otherdesired system. For example, the system 600 may take the form of adesktop computer, laptop computer, server, workstation, game consoles,embedded system, head-mounted display system, and/or any other type oflogic. Still yet, the system 600 may take the form of various otherdevices including, but not limited to a personal digital assistant (PDA)device, a mobile phone device, a television, etc.

Further, while not shown, the system 600 may be coupled to a network(e.g., a telecommunications network, local area network (LAN), wirelessnetwork, wide area network (WAN) such as the Internet, peer-to-peernetwork, cable network, or the like) for communication purposes.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of a preferred embodiment shouldnot be limited by any of the above-described exemplary embodiments, butshould be defined only in accordance with the following claims and theirequivalents.

What is claimed is:
 1. A system, comprising: a concave mirror element,wherein a concave surface of the concave mirror element faces anobserver; a diffuser holographic optical element (DHOE) located betweenthe observer and the concave mirror element; and a projector configuredto project light rays onto the DHOE, wherein the light rays are diffusedby the DHOE to the concave surface of the concave mirror element andreflected back to the observer such that the observer perceives avirtual image that appears to the observer at a position behind theconcave mirror element and further from the observer than the concavemirror element.
 2. The system of claim 1, further comprising a lightguide between the projector and the DHOE and configured to fold a pathof the light rays using internal reflection.
 3. The system of claim 2,wherein the light guide comprises a wedge-shaped waveguide.
 4. Thesystem of claim 1, wherein the projector faces the concave surface ofthe concave mirror element.
 5. The system of claim 1, wherein theprojector is located between the DHOE and the concave mirror element andfaces away from the concave surface of the concave mirror element. 6.The system of claim 1, wherein the concave mirror element comprises aconcave half-mirror configured to allow the observer to see through theconcave mirror element.
 7. The system of claim 1, wherein the concavemirror element comprises a concave mirror configured to block a scenebehind the concave mirror element from the observer.
 8. The system ofclaim 1, wherein the concave mirror element comprises awavelength-selective dichroic mirror configured to selectively reflect afirst wavelength and not reflect a second wavelength.
 9. The system ofclaim 8, wherein the projector is configured to produce the light waveshaving the first wavelength.
 10. The system of claim 1, wherein theprojector, DHOE, and concave mirror element are configured within anapparatus suitable for wearing over at least one eye of the observer.11. The system of claim 1, wherein the projector is located at a secondposition where a reference wave light source was used to record theDHOE.
 12. A method, comprising: generating an image by a projectionengine; and projecting light rays defining the image onto a diffuserholographic optical element (DHOE) located between an observer and aconcave mirror element, wherein the light rays are projected onto theDHOE at a reference angle that causes the light rays to be diffused to aconcave surface of the concave mirror element that faces the observer;and the diffused light rays are reflected back to the observer off theconcave surface of the concave mirror element such that the observerperceives a virtual image that appears to the observer at a positionbehind the concave mirror element and further from the observer than theconcave mirror element.
 13. The method of claim 12, further comprisingfolding a path of the light rays by a light guide located between theprojector and the DHOE.
 14. The method of claim 13, wherein the lightguide comprises a wedge-shaped waveguide.
 15. The method of claim 12,wherein a projector faces the concave surface of the concave mirrorelement and projects the light rays towards the concave surface of theconcave mirror element.
 16. The method of claim 12, wherein a projectoris located between the DHOE and the concave mirror element and projectsthe light rays away from the concave surface of the concave mirrorelement.
 17. The method of claim 12, wherein the concave mirror elementcomprises a concave half-mirror configured to allow the observer to seethrough the concave mirror element.
 18. The method of claim 12, whereinthe concave mirror element comprises a concave mirror configured toblock a scene behind the concave mirror element from the observer. 19.The method of claim 12, wherein the concave mirror element comprises awavelength-selective dichroic mirror configured to selectively reflect afirst wavelength and not reflect a second wavelength.
 20. The method ofclaim 19, wherein a projector produces the light waves to have the firstwavelength.